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From: Jacob Moody <moody@mail.posixcafe.org>
To: 9front@9front.org
Subject: Re: [9front] fix race condition on writes to #v/vgactl
Date: Tue, 16 Aug 2022 14:51:50 -0600	[thread overview]
Message-ID: <eaf696a0-a2cc-35bb-16ad-a46f9537fda3@posixcafe.org> (raw)
In-Reply-To: <E9ABB2B557B7868E845353FD9049ECAC@wopr.sciops.net>

On 8/16/22 14:44, qwx@sciops.net wrote:
> On Tue Aug 16 08:12:41 +0200 2022, qwx@sciops.net wrote:
>> Hello,
>> I've been experiencing a seemingly impossible kernel panic when
>> messing with vgactl.  Occasionally, writing multiple commands to
>> /dev/vgactl rapidly may cause an assert to fail
>> (/sys/src/9/port/devdraw.c:/assert).  The panic is perfectly
>> reproducible by sending `softscreen off' commands quickly (tested on
>> x61t):
>> 	; for(i in `{seq 10}) echo softscreen off >/dev/vgactl
>> The panic occurs within the first few iterations.  Moving some locks
>> out of individual functions to hold them for the entire step fixes
>> this.  The patch below works, but qunlock may be called without the
>> drawlock being held, I need to recheck and clean up before commiting
>> anything.  Credit to moody for suggesting looking in this direction!
> Here's the final patch, mostly the same.  I'll commit this later
> unless there are any objections.
> Thanks,
> qwx

Checks out to me.

  reply	other threads:[~2022-08-16 20:55 UTC|newest]

Thread overview: 9+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-08-16  6:12 qwx
2022-08-16 20:44 ` qwx
2022-08-16 20:51   ` Jacob Moody [this message]
2022-08-16 23:02   ` Anthony Martin
2022-08-17 12:10     ` qwx
2022-08-17 12:17       ` ori
2022-08-17 20:21         ` qwx
2022-08-18  2:23           ` ori
2022-08-18  5:36             ` qwx

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